Vigilance Key to Following Functional But 'Recalled' ICD Leads: Riata Summit Insights

January 26, 2012

January 27, 2012 (Minneapolis, Minnesota) — A tsunami can be barely visible above the water as it hurtles a potentially overwhelming wave of energy from below the surface. Are clinicians and patients facing a similar situation in the exposed wires and other issues coming to light with the "recalled" St Jude Medical Riata or Riata ST implantable cardioverter defibrillator (ICD) leads, the ones featuring all-silicone insulation?

One fear is that the currently identified Riata lead failures are but the leading edge of an oncoming wave, although one without a lot of data to counter it or back it up.

The evidence base grew a bit at last week's one-day, Riata ICD lead "summit," which provided some clues for answering the question of whether the initial cases herald a wavelet or tidal wave of affected patients

"There are still many unknown issues about the lead problem. Physicians need to balance [protecting] their patients' safety against the risks of generating anxiety and causing physical harm through discretionary lead extraction," according to Dr Ernest Lau (Royal Victoria Hospital, Belfast, UK), who emailed comments to heartwire . At the summit, Lau presented Riata follow-up data based on all Riata patients in Northern Ireland.

Reprise of Data From Northern Ireland

At the Riata summit, Lau reprised and elaborated on data his group had presented at the European Society of Cardiology (ESC) 2011 Congress. Their analysis involved 165 surviving patients among all those in Northern Ireland who received the problematic Riata leads (a mean of 3.98 years previously) and were invited to undergo fluoroscopic screening.

It revealed externalized conductors in 15%; in 1.8% the findings were "borderline," and externalizations could not be seen in 83%. Of the 25 patients with externalizations, 20 were identified only by fluoroscopy and five also had associated electrical issues. Seven patients underwent lead extraction.

But the clinicians-only meeting didn't settle many of the remaining questions. "With other lead recalls, we had a management plan, a plan for what we should do," according to Dr Edmund Keung (San Francisco Veterans Affairs Medical Center, CA), who directs the VA National Cardiac Device Surveillance Center. "This one--there are a lot of unknowns." As a result, Keung said in an interview, the Riata recall is regarded as far more serious than prior ICD-lead recalls, notably for the Medtronic Sprint Fidelis.

New Insights About Evolving Issues

In one retrospective series from seven major centers unveiled at the summit, the failure rate was 1.7 per patient-year for 773 patients with Riata leads (8F diameter) and only 0.64 per patient-year for 287 patients with slimmer (7F) Riata ST leads. Importantly, however, the mean time from lead implantation to failure averaged 4.3 years and 3.3 years, respectively, suggesting that the low Riata ST rate isn't necessarily inherent, but only the beginning.

The presenter of those initial findings from the Independent Multicenter Riata Study, Dr Raed H Abdelhadi (Minneapolis Heart Institute at Abbott Northwestern Hospital, MN), noted for heartwire that the failures are apparently due to erosion of the internal lead wires, or cables, through the outside silicone insulation, and the process seems to be continuous. As a result, goes the prevailing view, the likelihood that the cables will penetrate the insulation and be exposed, or "externalized," begins a few years after implantation and only becomes greater with time.

The silicone is worn though, the cables become free outside the body of the lead, and then it's like hanging out in a storm.

This is something to watch for, Abdelhadi said; if the externalizations and resulting electrical issues are time-dependent in that way, it's crucial to stay vigilant with those Riata recipients who so far have had no problems. Times from implant to failure have been approximately three to six years in different series. The last patients to receive the recalled St Jude leads in his analysis were implanted in in 2008.

"We don't know that it's time-dependent; we have not observed progression," Abdelhadi said to heartwire . "But it's a reasonable possibility, and we have to keep it in mind when we look at these patients." If the externalizations come from a time-dependent process, then there may indeed be a coming tsunami of Riata lead failures from the 80% to 90% of recipients who currently have no externalizations or have them but with no resulting electrical issues.

"I think in the absence of clear data, people often tend to speculate," electrophysiologist and St Jude vice president and chief medical officer Dr Mark D Carlson told heartwire . "That just emphasizes the importance of collecting data and doing it in a systematic fashion, not jumping to conclusions, and getting the data so we can make the appropriate decisions and recommendations."

Carlson pointed out that St Jude launched the prospective Riata Lead Evaluation Study in late 2011, which is aimed at identifying the prevalence of externalized conductors, any resulting malfunctions, and any associated clinical effects by following at least 500 patients with Riata or Riata ST leads. Any patient showing externalized conductors will be assessed every three months out to two years.

We don't really know the natural history of what happens to a lead with externalized conductors that function normally

"The most important consensus, and really the only clear consensus that came out of the meeting, was the need for more information," Carlson said, adding that St Jude encourages any physician who sees externalized Riata conductors to send them to the company for analysis.

Riata summit cochair Dr Robert G Hauser (Abbott Northwestern Hospital and Minneapolis Heart Institute, MN), who told heartwire that the meeting's discussions were the best yet on the problematic Riata leads, said "there was a general feeling that St Jude just hasn't done enough, they should have done more studies, sooner."

But Dr Richard G Trohman (Rush University Medical Center, Chicago, IL), one of the expert panelists at the summit, said, "I think St Jude's response to this has been transparent and responsible."

The Natural History of Externalizations

Whether erosion of the conductor silicone covering is an ongoing time-dependent process is central to the question of how many externalization cases are on the way. There's plenty of evidence that "the longer the lead is in service, the higher the risk of insulation breach," according to Lau, which is "more like a gradual than a sudden phenomenon and likely to progress over time."

He said insulation breach rates as high as 26% have been reported. "I think the rate of externalized conductors will be in the double-digit region, but the prevalence will vary from center to center and depend on multiple factors," such as specific lead model, time since implantation, patient features, and implantation technique.

"No matter what, you're following [Riata recipients] every three to six months," observed Trohman. "But no one knows what's going to happen to these leads in the future. We don't really know the natural history of what happens to a lead with externalized conductors that function normally," he said, echoing an oft-noted concern at the summit.

Not all lead-related electrical anomalies--notably, nonphysiologic noise--can be detected by a routine ICD check.

Keung cautioned that the Durata leads St Jude brought out to replace the Riata line should be closely watched, pointing out that the mortality curves for patients with and without problematic leads tend to separate at about four years following implantation. Under that timeline, Durata leads would not currently be having issues but possibly could--if beset by similar erosion problems--somewhere down the line. Carlson said the Durata has a thicker, more erosion-resistant silicone-plastic composite coating the company calls Optim, unlike the thinner silicone-only coating that seems to be related to the externalizations. It has other design differences, he said, including a soft, curved tip "for handling and performance" and smaller center coil. "These are very different leads." While some of those added features seem aimed at avoiding externalizations, others appear to address another problem that had previously emerged with Riata leads, perforation.

Veterans Affairs Riata Experience, Compared With Other Leads

In the Department of Veterans Affairs Riata experience, Keung reported at the summit, which focused not on cable externalizations but on lead failures defined as electrical abnormalities, the most common identified problem was "noise."

As reported by Keung, there were significant differences in the longevity of Riata leads compared with other ICD leads. Most failures, 63%, were associated with nonphysiologic noise with or without other abnormalities. Sometimes, noise read by ICDs as ventricular fibrillation (VF) failed to trigger automatic alerts. The study found that:

  • 32% of failure were associated with nonphysiological noise only.

  • 33% of noise-only failures didn't trip existing alert triggers.

In a small 24-patient cohort with abandoned Riata leads (not extracted but replaced), no inappropriate shocks or other adverse events were observed over a mean of 16.8 months.

Parameter Riata, n=1261 units (%) Quattro, n=6091 units (%) Sprint Fidelis, n=5072 units (%)
Non–perforation failure incidence 3.0 0.46 7.47
Failure rate per device year 0.78 0.15 2.08

Notably, the failure-alert systems used in the study as part of the internet-based remote monitoring network did not generally pick up on noise, by itself--it did not trigger automatic alerts. So, Keung said, the VA patients' systems were remotely interrogated every month instead of the usual three months, shortening the interval during which electrical noise would go undetected.

The Independent Multicenter Riata Study

In this large series, which included 1060 "fairly typical" patients who received Riata-equipped ICDs from 2002 to 2008, 70% have had no problems in the mean follow-up of more than four years. In 24% of cases, the leads have been replaced or abandoned after insertions of a new lead; 21% of the patients died. About 30% of the group had received appropriate ICD pacing therapy and 27% appropriate shocks.

But the combined Riata failure rate was much higher than reported rates for Medtronic Quattro leads.

Failure Rates for St Jude Riata, Riata ST, and (for Comparison) Medtronic Quattro ICD Leads in the Independent Multicenter Riata Study

All-cause failure Riata + Riata ST (n=1060) Riata alone (n=773) Riata ST alone (n=287) Medtronic Quattro* (n=1668)
Follow-up (y) 3.99 4.26 3.26 3.18
Failures (n) 62 56 6 23
Failures/patient-year (%) 1.47 1.70 0.64 0.43

*For comparison, from a three-center study

Failure defined as abnormal impedance; electrical noise; high defibrillation threshold requiring lead replacement; or externalized conductors on fluoroscopy or X-ray (regardless of normal or abnormal function)

As noted by Carlson, attendees at the meeting mostly agreed that more data are needed to guide management decisions, especially regarding how to handle patients with Riata leads who aren't having problems. It's not known, for example, whether to go ahead and screen all Riata recipients with fluoroscopy or whether to also then follow those patients with fluoroscopy.

Keung didn't think so before the summit and still doesn't days afterward. "A thing we learn in medicine is, don't do a test unless we know what to do with the results."

Indeed, Trohman said, "I'm not sure we came to a consensus. Some people felt, why look [for externalizations], because you're not really sure what to do and you just create a quandary for yourself."

Electrical Abnormalities Associated With Failed St Jude Riata and Riata ST Leads in the Independent Multicenter Riata Study

Abnormality % of 1060 cases
Noise/oversensing 51
Elevated pacing thresholds requiring lead replacement 33
Abnormal pacing impedance 27
Abnormal high voltage impedance 9
Decline in R wave requiring lead replacement 7
High defibrillation thresholds plus another electric abnormality leading to lead replacement 4

But Hauser said he believes there was an informal consensus that fluoroscopic screening of Riata recipients who haven't had issues is acceptable. That's consistent with Abdelhadi's impressions. He said "probably close to 70%" of members of the health professional–only audience, when polled, "thought that doing a fluoroscopy is probably a 'reasonable' thing.

"If you don't know [whether there are externalized wires], it's probably better to know than not know, even if you don't know exactly what to do with them. That's at least my feeling--so you can be more vigilant when you look at the electrical parameters and you can consult with the patient. I think the patient should probably know that there's something [going on] that's not supposed to be happening."

That's to some degree at odds with recommendations from St Jude, which the Heart Rhythm Society (HRS) has posted on its site, and which slant in the other direction: "The value of screening x-ray or fluoroscopy for patients with leads that exhibit no electrical abnormalities is unknown at this time, and therefore, the risk of increased radiation exposure for monitoring should be weighed against using remote monitoring and in-clinic follow-up for detection of electrical anomalies."

"I don't think those recommendations are wrong, but I don't think our approach to these leads is yet etched in stone," according to Trohman. "The story may evolve, and that's what I want to caution people about." he said. He said at his center they've had 71 patients with the problematic Riatas, but none have shown electrical abnormalities; however, both sets of Riata leads observed on chest X-ray were found to have externalized conductors. Still, a 71-patient population "is not huge."

As for whether to extract the leads, and from which patients, "there was some debate about whether it should be offered as an option," Trohman said. "I think we had a consensus that each case should be reviewed on an individual basis and that before a physician talks to a patient with externalized conductors, they should have a game plan in mind. But there was no consensus that you should offer it to everyone with the same zeal."

At the meeting, when the panelists were asked for their greatest fear regarding the Riata affair, Trohman said, "I said my greatest fear is that the current [St Jude and HRS] recommendations are relatively simple and not very alarmist, and that's good--but I'm worried that some people will be lulled to sleep by that and not follow [patients with the leads] more intensely. In spite of the fact that it doesn't look too bad at this point, watchful waiting should be the phrase of the day. I don't think we can say we know everything that we need to know or that we can say that this is not going to be a bigger problem in the future."

In fact, Hauser said, presentations at the summit collectively showed "that the Riata lead has a number of problems besides just externalized cables."

For example, "we learned that some of these [externalized] cables can break free and potentially cause some complications that we weren't aware of before." That insight came from members of the providers-only audience at the summit who rose to share case reports, Hauser said.

The Riata lead has a number of problems besides just externalized cables.

"I'm hearing more that the cables aren't just confined to one small area, they may totally escape from the body of the lead. We heard about some cables that came through a superior vena cava. One was in the pulmonary artery. Obviously we need to do more data collection and keep a closer eye on these patients than we thought previously."

The mechanisms behind the problem aren't known, Hauser said, "but you can picture it. These cables are under a lot of stress, beat to beat. They're relatively small cables. I think it's like any other mechanical situation: wear and tear." It starts with movement of the cables within the insulation, erosion, then externalization. "The silicone is worn though, the cables become free outside the body of the lead, and then it's like hanging out in a storm."

On the other hand, Lau said about migrating lead fragments, "We haven't seen such abnormalities, and they are probably very uncommon."

Keung cautioned, as did others on the panel, that there's a danger in focusing too tightly on what seems like the Riata's chief problem at this point. "We all concentrate on externalizations of the lead," he said. "We have this 3% [electrical] failure rate--can it all be explained by broken conductors? I don't think so; I think there may be more to it. We shouldn't look just at externalization and forget about other things."

Abdelhadi discloses that the study he presented was supported by research grants from the Minneapolis Heart Institute Foundation and Abbott Northwestern Hospital Foundation. Lau and Hauser had no disclosures. Trohman discloses having served on the speaker's bureau for Medtronic, St Jude Medical, and Boston Scientific; having been a consultant for Medtronic and Biosense Webster; and having received research funding from Medtronic, Biosense Webster, and Biotronik. Keung had no disclosures and said his comments reflect his own views, not those of the Department of Veterans Affairs.

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